Respiratory rate is a common physiological parameter in physiological parameters monitoring that is usually measured via impedance pneumography. Respiratory rate is generally calculated by following steps: detecting peaks and valleys from received waveform, calculating duration of each respiratory cycle and stacking the durations into an FIFO (First In, First Out) array, then averaging a number of durations of recent respiratory cycles, where the number is restricted by an accumulated time threshold.
The respiratory rate of a patient may change frequently, because the patient's respiratory impedance can be sensitive to some external factors, such as movement, heart beat and the like. When the respiratory rate of the patient changes from low to high (or from high to low) very quickly and then enters into a relatively stable respiratory state, it is generally desirable that the respiratory rate detected by a patient monitor could reflect the changing respiration trend in a timely manner. But conventional respiratory rate smoothing calculation method may not meet such requirements satisfactorily, and specific problems can be as follows.
1. The respiratory rate is calculated by averaging real-time respiratory rates of several respiratory cycles without considering real-time change in the respiratory rate, so the result may not reflect real-time condition; and
2. In conventional methods, the respiratory rate is calculated using real-time respiratory rates of the latest 12 respiratory cycles without fully considering the influence of respiratory cycles used, which may cause poor smoothness in the result, for example, sudden change can occur in current respiratory rate when real-time respiratory waveform is interfered.